In the formation of plastic sealing liners in the shells of container closures of various types such as crown caps or screw caps, it is a general practice to cut charges of plastic as it is extruded from an extruder and to dispense the individual charges into successive shells as they pass in single file below the extruder. Devices of this type are disclosed, for example, in U.S. Pat. Nos. 3,360,827 and 4,060,053. In construction, the extruder of these devices includes an extrusion block disposed at the front end of the extruder and having a flat surface through which an extrusion opening extends. By the action of a cutting blade rotating across the opening end of the extrusion opening, dispensing of the cut charge of the plastic to a predetermined position within a shell is effected. The filled shell is then carried to a location where the plastic in the shell is molded into the desired shape.
A conventional cutting and dispensing device includes a rotating shaft extending substantially perpendicular to the flat surface of the extrusion block with its front end positioned opposite to the flat surface of the block. At the front end of this shaft, a cutting tool is mounted such that a cutting blade formed on the front surface of the tool is rotated across the open end of the extrusion opening. The cutting tool is mounted on the front end of the rotating shaft by a connection at the back surface of the cutting tool with the shaft extending substantially perpendicular to the flat surface of the extrusion block. Spring means are employed by urging the shaft and thus the cutting tool and blade against the flat surface of the extrusion block. Accordingly, the cutting blade formed on the front surface of the cutting tool is brought into resilient contact with the flat surface of the extrusion block by the action of the spring, and is rotated across the open end of the extrusion opening by rotational action transmitted to the cutting tool by the rotating shaft.
In order to properly cut the plastic extruded from the extrusion opening in this type of apparatus and to properly dispense a predetermined amount of the cut plastic to a predetermined position within a shell, it is important that the entire flat cutting edge of the cutting blade make linear contact with the flat surface of the extrusion block. Otherwise, the resin will not be cut well and the time required for cutting will become somewhat longer and cause errors in the amount and position of the plastic dispensed into the shell. In particular, when the cutting blade is rotated at high speed and the cutting and dispensing of the plastic by means of the cutting blade are carried out at high speed, any increase in the time required for cutting the resin by the cutting blade would cause considerable errors in the amount and position of the resin dispensed to the shell.
In order to bring the entire flat cutting edge of the cutting blade into linear contact with the flat surface of the extrusion block, it is necessary in principle to dispose the rotating shaft fully perpendicular to the flat surface of the extrusion block, form the connection on the back surface of the cutting tool perpendicular to the cutting edge on the front surface of the cutting tool, and to also mount the cutting tool on the front end of the rotating shaft with its cutting edge precisely perpendicular to the axis of rotation of the rotating shaft. As can be readily appreciated, it is extremely difficult, it not sometimes impossible, to meet all of these requirements. Accordingly, in the conventional plastic cutting apparatus, the entire flat cutting edge of the cutting blade does not generally make sufficiently, good linear contact with the flat surface of the extrusion block, and this frequently causes errors in the amount and position of the resin dispensed to shells. Moreover, because the cutting blade does not make contact with the surface of the extrusion block as prescribed, the cutting blade undergoes localized wear, and its life is relatively short.
In some conventional plastic cutting apparatus, the cutting tool is mounted such that it may tilt in a predetermined direction with respect to the front end of the rotating shaft at its connection to the rotating shaft. In such a structure, the error in the mounting of the rotating shaft, the error in the connection between the shaft and cutting tool, etc. can be partially corrected by this tilting. The errors, however, can be corrected only in a very limited region in a predetermined direction in which the tool can tilt. The aforesaid problem, therefore, remains essentially unsolved. If the cutting tool were mounted such that it could tilt in any direction with respect to the front end of the rotating shaft, the aforesaid errors would be able to be fully corrected. But in conventional apparatus, the direction of tilting of the cutting tool with respect to the rotating shaft is necessarily limited to a predetermined one because the rotation of the rotating shaft must be transmitted to the mounting base through its connection to the cutting tool. Consequently, it is impossible with present constructions to make the cutting tool tilt in any desired direction with respect to the front end of the rotating shaft.
In addition to the above problem, in the conventional plastic cutting apparatus, a mounting base for connection of the cutting tool to the rotating shaft must extend substantially perpendicularly to the cutting blade and along the axis of rotation of the rotating shaft. Thus, it must be formed precisely on the back surface of the cutting tool whose front surface has a flat cutting edge formed therein. This naturally leads to an increased cost of production of the cutting tool.